The invention relates to a process for producing patterned or structured protective and insulating layers.
In order to protect microelectronic and optoelectronic components against external influences, such as moisture, the components are initially provided with a patterned or structured buffer layer (xe2x80x9cbuffer coatingxe2x80x9d) and then with a molding or potting compound. Due to distinct cost advantages during patterning or structuring, photosensitive materials are preferred to non-photosensitive materials in the fabrication of the buffer layers. In particular, in the case of optoelectronic components, sufficient transparency of the buffer layer (as well as of the potting compound) is very important. However, even in microelectronic components, which do not require a transparent molding compound, good transparency of the buffer layer is important because a marking which is applied in order to distinguish between good and bad chips is easier to identify given a transparent material.
Polyimides, which are fabricated by heat-treating or tempering photosensitive polyimide precursors, have been used heretofore as a material for buffer layers (see the book entitled xe2x80x9cPolymers in Microelectronicsxe2x80x94Fundamentals and Applicationsxe2x80x9d, by D. S. Soane and Z. Martynenko, Elsevier, Science Publishers B. V., Amsterdam 1989, pages 1 to 13). However, polyimides of that type do not have a sufficient transparency (after the heat-treatment). Moreover, for patterning or structuring of the precursors, it is necessary to work according to the negative mode and the development must be effected by using organic solvents.
It is accordingly an object of the invention to provide a process for producing patterned or structured protective and insulating layers, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known processes of this general type and which permits the production of structured protective and insulating layers, in particular buffer layers, that have above all a high transparency, in addition to a high resolution and a low absorption of moisture.
With the foregoing and other objects in view there is provided, in accordance with the invention, a process for producing or fabricating structured or patterned protective and insulating layers, which comprises applying a solution of a photosensitive polyhydroxyamide or polyhydroxyimide to a substrate, which is a wafer, in particular, and drying to form a layer; structuring or patterning the layer by irradiation with UV light or X-rays using a mask or guidance of a UV or electron beam and subsequent aqueous-alkali development; and whole-area irradiating the structured or patterned layer with UV light and then tempering or heat-treating.
The process according to the invention, which serves in particular for the fabrication of buffer layers, furnishes layers including polybenzoxazole (PBO) or polyhydroxyimide. Photosensitive PBO precursors are used, namely photosensitive polyhydroxyamides, in order to fabricate layers of polybenzoxazole. These PBO precursors are photopatterned, for example through the use of a mask, and heat-treated or tempered, with cyclization to form the polybenzoxazole being effected.
What is essential in the process according to the invention is the fact that the heat-treatment is preceded by whole-area irradiation, so-called flood exposure, that is to say irradiation without a mask. The effect which is surprisingly achieved thereby is that the polymers obtained after the heat-treatment have high transparency. In comparison with polyimides, these polymers, which have high temperature stability, afford the further advantage of permitting the precursors to be patterned or structured according to the positive mode and to be developed in an aqueous-alkaline manner. Moreover, the absorption of moisture is lower in the case of polybenzoxazole.
The following measures have proved to be advantageous in the production of the structured or patterned protective and insulating layers according to the invention.
In accordance with another mode of the invention, the whole-area irradiation is carried out with a higher radiation dose than the patterning or structuring irradiation.
In accordance with a further mode of the invention, the UV light is used for the patterning or structuring irradiation and for the whole-area irradiation, in particular UV light having a wavelength xcex greater than 200 nm.
In accordance with an added mode of the invention, the patterning or structuring irradiation with UV light, for example using a laser, is carried out with a radiation dose of 200 to 2000 mJ/cm2.
In accordance with a concomitant mode of the invention, the heat-treatment or tempering is effected at a temperature Txe2x89xa7250xc2x0 C.
The radiation dose is preferably 1 to 100 mJ/cm2 in the event of irradiation with X-rays, and preferably 10 to 1000 xcexcC/cm2 in the event of irradiation with electron beams.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a process for producing patterned or structured protective and insulating layers, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and process for operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying examples.